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GATE CSE 2026 Session 2 Q41: Shift-reduce conflicts in the LR(0) table of a grammar

Question

Consider the canonical LR(0)LR(0) parsing of the grammar below using terminals {a,b,c}\{a, b, c\} and non-terminals {A,B,C,S}\{A, B, C, S\} with SS as the start symbol.

S→ACBA→aA∣ϵC→cC∣ϵB→bB∣b\begin{aligned} S &\rightarrow ACB \\ A &\rightarrow aA \mid \epsilon \\ C &\rightarrow cC \mid \epsilon \\ B &\rightarrow bB \mid b \end{aligned}

Which one of the following options gives the number of shift-reduce conflicts that will occur in the LR(0)LR(0) ACTION table?

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Answer: D (official GATE 2026 final answer key)

Concept used: In LR(0), a complete item forces a reduce on every terminal, clashing with any shift in the same state.

First step: Build the LR(0) item sets; states containing A→⋅A \rightarrow \cdot or C→⋅C \rightarrow \cdot or B→b⋅B \rightarrow b\cdot alongside shift items are the conflict candidates, counted per terminal entry.

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Source: official GATE 2026 Session 2 CS question paper and final answer key, organised by IIT Guwahati. Question paper · Answer key

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